Step 1
Combine rhubarb and sugar for topping in a large bowl. Mix to combine and set aside for about 1 hour to allow the rhubarb to draw juice.
Step 2
Beat butter and sugar for base until light and fluffy. Add flour wine baking powder and egg; swiftly knead until it comes together to form a disc. Wrap in plastic wrap and place in the refrigerator for 5 to 10 minutes.
Step 3
Preheat the oven to 350 degrees F (175 degrees C). Grease a 9-inch springform cake pan.
Step 4
Roll out the base on a lightly floured surface into a circle slightly larger than the diameter of the cake pan. Transfer to the prepared cake pan letting the dough come up the sides by about 1 inch.
Step 5
Drain rhubarb topping and evenly scatter over the base.
Step 6
Bake in the preheated oven for 45 minutes.
Step 7
Meanwhile beat together almond flour 3/4 cup plus 2 tablespoons creme fraiche sugar eggs vanilla sugar and cinnamon for almond custard until smooth.
Step 8
Remove cake from oven after 45 minutes of baking. Top with almond mixture and use a spatula to spread it evenly to the sides of the pan. Return to the oven and bake until the top of the cake is golden brown about 30 minutes more.
Step 9
Remove from the oven and let cool in the pan before slicing.